Sealing means for electrically driven water purification units and method of manufacturing thereof

ABSTRACT

An electrically driven membrane process apparatus is provided comprising a first spacer having a perimeter having a surface with an inner peripheral edge defining an opening, and a recess formed on the inner peripheral edge, and an ion exchange membrane having an outer edge fitted within the recess. The spacer can further comprise a plurality of bosses and an ion exchange membrane having a corresponding plurality of apertures for receiving the bosses. The spacer can include a plastic mesh consisting essentially of polypropylene or polyethylene, and a perimeter surrounding the plastic mesh, the perimeter comprising material selected from the group consisting of thermoplastic vulcanizates and thermoplastic elastomeric olefins. The spacer can have an upstanding seal member depending therefrom, received by groove within a corresponding frame member. A second spacer is also provided having a continuous flange depending from its surface and surrounding a throughbore, for pinching a portion of the first spacer. A method of injection molding a thin plastic part comprising a perimeter having an inner peripheral edge and a mesh joined to the inner peripheral edge is also provided including the steps of (a) providing first and second mold halves, each of the mold halves having an interior surface and a continuous ridge depending therefrom; and (b) pinching opposite side of the mesh between the ridges to form a flow barrier.

RELATED APPLICATIONS

[0001] This is a Continuation-in-Part Application of U.S. patentapplication Ser. No. 09/327,598, filed Jun. 8, 1999.

FIELD OF THE INVENTION

[0002] The present invention relates to electrically driven waterpurification devices and, in particular, to novel sealing means tofacilitate sealing of such devices.

DESCRIPTION OF THE RELATED ART

[0003] Water purification devices of the filter press type which purifywater by electrically driven membrane processes, such as electrodyalisisor electrodeionization, comprise individual chambers bounded by ionexchange membranes. Typically, each of the chambers is defined on oneside by a membrane disposed to the preferential permeation of dissolvedcation species (cation exchange membrane) and on an opposite side by amembrane disposed to the preferential permeation of dissolved anionspecies (anion exchange membrane).

[0004] Water to be purified enters one chamber commonly referred to as adiluting chamber. By passing a current through the device, electricallycharged species in the diluting chamber migrate towards and through theion exchange membranes into adjacent chambers commonly known asconcentrating chambers. As a result of these mechanisms, water exitingthe diluting chamber is substantially demineralized. Electricallycharged species which permeate through the ion exchange membranes andinto a concentrating chamber are flushed from the concentrating chamberby a separate aqueous stream flowing through the concentrating chamber.

[0005] To this end, the above-described devices comprise alternatingdiluting and concentrating chambers. In addition, cathode and anodechambers, housing a cathode and an anode respectively therein, areprovided at the extreme ends of such devices, thereby providing thenecessary current to effect purification of water flowing through thediluting chamber.

[0006] For maintaining separation of associated cation and anionexchange membranes, spacers are provided between the alternating cationand anion exchange membranes of the above-described water purificationdevices. Therefore, each of the diluting chambers and concentratingchambers of a typical electrically-driven water purification devicecomprise spacers sandwiched between alternating cation and anionexchange membranes.

[0007] To prevent any appreciable leakage from diluting chambers andconcentrating chambers of such devices, the above-described arrangementof spacers sandwiched between ion exchange membranes must form asubstantially water-tight seal. To this end, the spacers and the ionexchange membranes are pressed together and fixed in position with knownconnectors. Unfortunately, this alone has not provided adequate sealingcharacteristics.

[0008] Various attempts have been made to improve the sealingcharacteristics of electrically driven water purification devices. Forinstance, it is known to use an adhesive to bond the ion exchangemembranes to either side of a spacer. Unfortunately, as a result ofexposure to typical operating conditions, the seal formed thereby isprone to leakage, thereby causing the loss of valuable product water.This arises from the intrinsic moisture permeability of the IX membranesand because of poor mechanical sealing characteristics.

[0009] Alternatively, it is known to provide spacers having resiliento-ring type sealing members on either side of the spacer for engaging anopposing planar surface of adjacent spacers. A cation exchange membraneand an anion exchange membrane are pressed against opposite sides of thespacer and function as permselective barriers. In this arrangement, thespacer, its o-ring type sealing member, and ion exchange membranesdefine a space wherein ionic species in aqueous fluid media containedtherein can migrate in a direction substantially orthogonal to the planeof the spacer and permeate through either of the ion exchange membranes.Unfortunately, during assembly of the device, it is known to bedifficult to maintain ion exchange membranes in a desired alignmentrelative to associated spacers. Further, during operation and consequentexposure to relatively high internal pressure or differential pressureswithin the device, ion exchange membranes may move and become displacedfrom a desired position relative to their associated spacers. Failure tomaintain such a desired position may compromise the sealing of theassociated chamber.

[0010] In an attempt to limit movement of ion exchange membranes duringassembly of the water purification device, ion exchange membranes havebeen provided with alignment holes which receive fixed rod-likestructures. However, this provides a further potential source forleakage and, therefore, compromises sealing of the device.

[0011] The material of construction of known spacers is also known to bedetrimental to the sealing characteristics of this arrangement. Tofacilitate mass production by injection moulding, spacers are typicallymanufactured from thermoplastic materials, such as polypropylene.Unfortunately, such thermoplastic materials are prone to stressrelaxation or compression set. As a result, over time, because ofexposure to the relatively high internal pressures, such spacers, andparticularly their o-ring type sealing members, lose their resiliency,thereby compromising their ability to maintain adequate seals withadjacent surfaces.

SUMMARY OF THE INVENTION

[0012] According to one aspect, the present invention provides anelectrically driven membrane process apparatus comprising a first spacerhaving a perimeter having a surface with an inner peripheral edgedefining an opening, and a recess formed on the inner peripheral edge,and an ion exchange membrane having an outer edge fitted within therecess. The recess can be continuous along the inner peripheral edge.The ion exchange membrane can have a top surface wherein the top surfaceis vertically disposed no lower than the surface of the perimeter whenthe ion exchange membrane is fitted in the recess. The spacer can becomprised of material selected from the group consisting ofthermoplastic vulcanizates, thermoplastic elastomeric olefins andfluoropolymers. The spacer can be a concentrating chamber spacer(C-spacer) or a diluting chamber spacer (D-spacer).

[0013] In another aspect, the present invention provides an electricallydriven membrane process apparatus comprising a spacer with a pluralityof bosses and an ion exchange membrane having a corresponding pluralityof apertures for receiving the bosses. The spacer can further comprise aperimeter having a surface with an inner peripheral edge defining anopening, and a recess formed on the inner peripheral edge for fitting anion exchange membrane, wherein the bosses extend from the recesssubstantially perpendicular thereto.

[0014] In yet another aspect, the present invention provides a spacer ofan electrically driven membrane process apparatus comprising a plasticmesh consisting essentially of polypropylene or polyethylene, and aperimeter surrounding the plastic mesh, the perimeter comprisingmaterial selected from the group consisting of thermoplasticvulcanizates and thermoplastic elastomeric olefins.

[0015] In a further aspect, the present invention provides anelectrically driven water purification apparatus having a first spacerand a frame member separated by an ion exchange membrane, the firstspacer having an upstanding seal member depending therefrom and theframe member having a groove for receiving the seal member. The sealmember can be an o-ring or a sealing bead. The frame member can be asecond spacer, or cathode or anode end frames.

[0016] In another aspect, the present invention provides an electricallydriven membrane process apparatus having a first spacer and a framemember separated by an ion exchange membrane, the first spacercomprising a first surface having a first throughbore for flowing anaqueous liquid, the frame member comprising a second surface, a secondthroughbore extending through the second surface and communicating withthe first throughbore, and a continuous flange depending from the secondsurface and surrounding the second throughbore, the flange pinching aportion of the first surface surrounding the first throughbore. Thesecond throughbore can facilitate D-flow.

[0017] In a further aspect, the present invention provides anelectrically driven membrane process apparatus comprising anelectrically driven membrane process apparatus comprising a first spacerhaving a first perimeter having a surface with a first inner peripheraledge defining a first opening, a recess formed on the first innerperipheral edge, and a mesh extending across the first opening andjoined to the first inner peripheral edge, a second spacer having asecond perimeter having a surface with a second inner peripheral edgedefining a second opening, an ion exchange membrane fitted within therecess and extending across the first opening and having a surfaceportion engaged to the second perimeter inwardly of the first innerperipheral edge, and a ridge depending from the second perimeter of thesecond spacer and compressing the surface portion of the ion exchangemembrane against the mesh, thereby preventing or reducing likelihood ofbuckling of the mesh.

[0018] In yet another aspect, the present invention provides a method ofinjection molding a thin plastic part comprising a perimeter having aninner peripheral edge and a mesh joined to said inner peripheral edge,including the steps of (a) providing a mold having a cavity and a core,the cavity having a first interior surface and a first continuous ridgedepending from the first interior surface, the core having a secondinterior surface and a second continuous ridge depending from the secondinterior surface; and (b) pinching opposite side of the mesh between theridges to form a flow barrier. The cavity can further include hangingpins depending from the first interior surface. In this respect, themethod would then further include, after step (a) and before step (b),the step of suspending the mesh from the hanging pins.

BRIEF DESCRIPTION OF DRAWINGS

[0019] The present invention will be better understood with reference tothe appended drawings in which:

[0020]FIG. 1 is an exploded perspective view of an electrically drivenwater purification unit of the present invention;

[0021]FIG. 2a is a plan view of one side of a C-spacer of the presentinvention;

[0022]FIG. 2b is a sectional elevation view of the C-spacer of FIG. 2ataken along lines A-A;

[0023]FIG. 3 is a perspective view of an ion exchange membrane of thepresent invention;

[0024]FIG. 4a is a plan view of one side of a D-spacer of the presentinvention;

[0025]FIG. 4b is an elevation view of the D-spacer shown in FIG. 4a;

[0026]FIG. 5 is a plan view of one side of a D-spacer of the presentinvention, partly in section, illustrating flow channels formed therein;

[0027]FIG. 6 is a plan view of one side of an anode end frame of thepresent invention;

[0028]FIG. 7 is an illustration of an unclamped mold having meshinterposed between its cavity and core plates for purposes of injectionmolding;

[0029]FIG. 8 is a plan view of the exterior side of the cavity plate ofthe mold shown in FIG. 7;

[0030]FIG. 9 is a plan view of the interior side of the cavity plate ofthe mold shown in FIG. 7;

[0031]FIG. 10 is a plan view of the interior side of the core plate ofthe mold shown in FIG. 7;

[0032]FIG. 11 is an illustration of a second unclamped mold having meshinterposed between its cavity and core plates for purposes of injectionmolding a spacer of the present invention;

[0033]FIG. 12 is a plan view of the interior side of the cavity plate ofthe mold shown in FIG. 11;

[0034]FIG. 13 is a plan view of the interior side of the core plate ofthe mold shown in FIG. 11;

[0035]FIG. 14 is a plan view of the exterior side of the cavity plate ofthe mold shown in FIG. 11;

[0036]FIG. 15 is an illustration of an embodiment of a boss of aC-spacer;

[0037]FIG. 16 is an illustration of another embodiment of a boss of aC-spacer; and

[0038]FIG. 17 is an illustration of an embodiment of a secondary sealmember of a C-spacer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0039] The present invention provides a spacer of a filter press typeelectrically driven water purification apparatus, such as anelectrodyalisis unit or an electrodeionization unit. Electrodeionizationunits include those with ion exchange resin in the concentratingchamber. The spacer of the present invention can also be used in otherelectrically driven membrane process apparati of the filter press type.An example of another electrically driven membrane process which fallswithin the purview of this invention is salt splitting. The inventionwill hereafter be explained with reference to an electrically drivenwater purification apparatus.

[0040] Referring to FIG. 1, a typical electrically driven waterpurification apparatus 2 comprises alternating anion exchange membranes4 and cation exchange membranes 6. Spacers 10 and 100 are provided inbetween the alternating cation and anion exchange membranes to helpdefine alternating diluting chambers (“D-chambers”) and concentratingchambers (“C-chambers”). Electrode chambers, namely a cathode chamberwith a cathode 230 and an anode chamber with an anode 232, are providedat terminal ends of the unit, and are each bound on one side by a spacer10 and on an opposite side by an end plate 200 a or 200 b. To assemblethe water purification apparatus, each of the anion exchange membranes,cation exchange membranes, and associated spacers and end plates 200 aand 200 b are forced together to create a substantially fluid tightarrangement.

[0041] Different spacers are provided for each of the D-chambers andC-chambers. In this respect, the D-chamber spacer, or “D-spacer”, helpsdefine the D-chamber. Similarly, the C-chamber spacer, or “C-spacer”,helps define the C-chamber.

[0042] Referring to FIGS. 2a and 2 b, the C-spacer 10 comprises acontinuous perimeter 12 of thin, substantially flat elastomericmaterial, having a first side surface 14 and an opposite second sidesurface 15, and defining an opening 16. In this respect, the C-spacerhas a picture frame-type configuration. The C-spacer 10 is comprised ofa material which is not prone to significant stress relaxation whileable to withstand typical operating conditions in an electrically drivenwater purification unit. In particular, the C-spacer material shouldpossess acceptable electrical insulation properties and be chemicallyresistant to high and low pH levels. In this respect, an example ofsuitable materials include thermoplastic vulcanizates, thermoplasticelastomeric olefines, and fluoropolymers. The C-spacer 10 can bemanufactured by injection moulding or compression moulding.

[0043] The first side surface 14 can be pressed against an ion exchangemembrane, such as a cation exchange membrane 6. Similarly, the oppositesecond side surface 15 can be pressed against a second ion exchangemembrane, such as an anion exchange membrane 4. In one embodiment, theion exchange membrane associated with a side surface of the C-spacer 10is also associated with a side surface of the D-spacer 100 (see FIG. 4)in the manner described below. FIG. 3 shows one side surface of an ionexchange membrane 4 or 6, and it is understood that the features of oneside surface are the same as those of the opposite side surface.Further, FIG. 3 is representative of either an anion exchange membrane 4or a cation exchange membrane of the present invention. In anotherembodiment, the ion exchange membrane associated with a side surface ofthe C-spacer 10 is also associated with a side surface of an electrodeend plate 200 (see FIG. 6), such as a cathode end plate or an anode endplate (anode end plate is shown in FIG. 6), in the manner describedbelow.

[0044] Notably, pressing first and second ion exchange membranes againstthe first and second sides of the C-spacer 10 forms a C-chamber. Theinner peripheral edge 18 of the C-spacer 10 perimeter helps define aspace 16 which functions as a fluid passage for aqueous liquid flowingthrough the C-chamber.

[0045] First and second spaced-apart throughbores are provided in theC-chamber to facilitate flow in and out of the C-chamber. In oneembodiment, first and second throughbores can be formed in one or bothof the first and second ion exchange membranes (see FIG. 3) tofacilitate flow in and out of the C-chamber. In this respect, flow isintroduced in the C-chamber via the first throughbore 4 a or 6 a and isdischarged from the C-chamber via the second throughbore 4 b or 6 b(supply flow to and discharge flow from C-chamber hereinafter referredto as “C-flow”).

[0046] It is understood that other arrangements could also be providedto effect flow in and out of the C-chamber. For instance, the C-spacerperimeter 12 could be formed with throughbores and channels wherein thechannels facilitate fluid communication between the throughbores and theC-chamber. In this respect, aqueous liquid could be supplied via aninlet throughbore in the C-spacer perimeter, flow through a first set ofchannels formed in the C-spacer perimeter into the C-chamber, and thenleave the C-chamber through a second set of channels formed in theC-spacer perimeter which combine to facilitate discharge via an outletthroughbore formed in the C-spacer perimeter.

[0047] A first throughbore 20 and a second throughbore 22 extend throughthe surface of the C-spacer perimeter. The first throughbore 20 providesa fluid passage for purified water discharging from the D-chambers, thesecond throughbore 22 provides a fluid passage for water to be purifiedsupplied to the D-chambers (supply flow to and discharge flow fromD-chamber hereinafter referred to as “D-flow”). As will be describedbelow, means are provided to isolate C-flow from D-flow.

[0048] Throughgoing holes 24, 25 a and 25 b are also provided in theperimeter of the C-spacer 10. Holes 24 a, 24 b are adapted to receivealignment rods which assists in aligning the D-spacer when assembly thewater purification apparatus. Holes 25 a and 25 b are adapted to flowaqueous liquid discharging from the anode and cathode chambers.

[0049] In one embodiment, the C-spacer 10 can further comprise a plasticscreen or mesh 26 joined to the inner peripheral edge 18 of theperimeter 12 and extending through the space 16 defined by the innerperipheral edge 18 of the perimeter 12. The mesh 26 can be made integralwith or encapsulated on the inner peripheral edge 18 of the perimeter12. The mesh 26 further assists in spacing the anion exchange membranefrom the cation exchange membrane. The mesh 26 can be a bi-planar,non-woven high flow mesh. Alternatively, the mesh 26 can be woven.Suitable materials include polypropylene and polyethylene. It isunderstood that, where ion exchange resin is provided in theconcentrating chamber, no mesh would be required as the resin itselfwould provide a spacing function.

[0050] In one embodiment, mesh 26 comprises three co-planar layers ofpolypropylene mesh wherein the first and third layers have a thicknessof {fraction (20/1000)} of an inch and are characterized by 16 strandsper inch, and the second layer, interposed between the first and thirdlayers, has a thickness of {fraction (30/1000)} of an inch and ischaracterized by 15 strands per inch. Preferably, the first and thirdlayers of mesh are thinner and characterized by a tighter weave than thesecond layer. In this way, desirable hydraulic characteristics can beachieved (as the water flows primarily across the middle second layer)while the thinner outer layers with the tighter weaver provide desiredsupport to the membrane. In another embodiment, the second layer ischaracterized by a different colour or shading than the first and thirdlayers to permit easier identification and differentiation between thesecond and the first and third layers, thereby facilitating assembly.

[0051] Where the C-spacer 10 includes mesh 26 for spacing anion exchangemembranes from cation exchange membranes, the mesh 26 must be comprisedof material which are stable at high temperatures and chemicallyresistant to high and low pH environments. The material comprising theperimeter 12 must also be compatible with the material comprising mesh26 in regard to the manufacture of a unitary component comprising boththe perimeter 12 and mesh 26. In this respect, to facilitate meltprocessing of the C-spacer 10, the perimeter 12 is preferably comprisedof material which is melt processible at temperatures which would notcause degradation of the mesh. In this respect, where the mesh iscomprised of polypropylene or polyethylene, acceptable materials includethermoplastic vulcanizates and thermoplastic elastomeric olefines.

[0052] In the embodiment illustrated in FIG. 2, discontinuities or gaps28 may be provided between the mesh 26 and the perimeter 12 wherein suchdiscontinuities 28 correspond with the first and second throughbores ofan ion exchange membrane. Such discontinuities 28 provide visualassistance in properly aligning the ion exchange membrane in relation tothe C-spacer 10 during assembly of the water purification unit.

[0053] A side surface of the C-spacer further has a recess 30 formedtherein which is adapted for fitting an ion exchange membrane. When theion exchange membrane is fitted in the recess 30, the exposed surface ofthe ion exchange membrane is planar with the surface of the perimeter 12or slightly raised above the surface of the perimeter 12. In oneembodiment, a continuous recess 30 is provided along the innerperipheral edge 18 of the perimeter 12 and on both the first and secondside surfaces of the perimeter 12. During assembly of the waterpurification apparatus, the outer edge of ion exchange membrane isfitted in the recess 30 on the first side of the perimeter 12 and acation exchange membrane is positioned in the recess 30 on the secondside of the perimeter 12. The recesses 30 are sized to facilitate arelatively tight fitting arrangement between the ion exchange membranesand the perimeter and the ion exchange membranes and the mesh, once theion exchange membranes and C-spacer 10 are forced together and once theion exchange membranes become hydrated and swell.

[0054] A side surface of the C-spacer 10 further includes a plurality ofbosses 32 which can be fitted within corresponding apertures 8 of an ionexchange membrane. Corresponding apertures can be provided in a D-spacer100 or an electrode end plate 200 to receive insertion of the bosses 32.In one embodiment, the bosses 32 extend along the inner peripheral edge18 of the perimeter 12 on both the first and second side surfaces of theperimeter 12. More preferably, the bosses 32 extend from the surfaces ofthe recessed portions 30 substantially perpendicular thereto. Duringassembly of the water purification apparatus, the bosses 32 on the firstside of the perimeter 12 are matched with corresponding mating apertures8 in the anion exchange membrane 4 and the D-spacer 100 or electrode endplate 200. The apertures 8 of the anion exchange membrane 4 and a firstD-spacer 100 are then fitted over the corresponding bosses 32.Similarly, the bosses 32 on the second side of the perimeter 12 arematched with corresponding apertures 8 in the cation exchange membrane 6and a second D-spacer 100 or an electrode end plate 200. The aperturesof the cation exchange membrane 6 and the second D-spacer 100 orelectrode end plate 200 are then fitted over the corresponding bosses32. The apertures 8 of the ion exchange membranes 4 or 6 are sized to betightly fitted over the bosses 32. In one embodiment, the apertures 8are sized to be no greater than approximately 75% of the diameter of thebosses 32.

[0055] Referring to FIGS. 15 and 16, in one embodiment, the bosses 32include a radially extending undercut 33. Further, sidewall surface 35of the bosses 32 can be tapered or flared outwardly from top surface 37towards undercut 33, to facilitate insertion of bosses 32 throughapertures 8 in membranes 4 or 6.

[0056] An upstanding secondary seal member 34 is also provided on a sidesurface of the C-spacer 10 for fitting within a first correspondinggroove of a D-spacer 100 or electrode end plate 200. In one embodiment,the secondary seal member 34 is a continuous O-ring or bead extendingfrom and integral with the surface of the C-spacer. The secondary sealmember 34 depends from the surface of the perimeter 12. In oneembodiment, secondary seal members 34 are provided on both the first andsecond side surfaces of the perimeter 12. The secondary seal member 34on the first side surface and the secondary seal member 34 on the secondside surface each fit within grooves of a first D-spacer 100 and asecond D-spacer 100 or electrode end plate 200 respectively. Duringassembly of the water purification apparatus, the secondary seal members34 are fitted or inserted into the grooves of the D-spacers 100 andelectrode end plates 200.

[0057] Referring to FIG. 17, in one embodiment, secondary seal member 34is characterized by a ratio of width:height of about 3:2. In anotherembodiment, the ratio of width:height is from about 1.25:1 to 2:1.

[0058] Referring to FIG. 4a and 4 b, the D-spacer 100 comprises acontinuous perimeter 102 of a thin plastic material, having a first sidesurface 104 and an opposite second side surface 105 and defining anopening 106. In order to complement the sealing features provided on theabove-described embodiment of the C-spacer 10, and therefore improvessealing of both the C-chamber and the D-chamber, the D-spacer 100 ismade of harder material than the C-spacer 10. Suitable materials for theD-spacer 100 include polyethylene and polypropylene.

[0059] The first side surface of the D-spacer 100 can be pressed againstan ion exchange membrane, such as a cation exchange membrane 6.Similarly, the second side surface of the D-spacer 100 can be pressedagainst a second ion exchange membrane, such as an anion exchangemembrane 4. In one embodiment, one of the ion exchange membranesassociated with a side surface of the D-spacer 100 is also associatedwith a side surface of the C-spacer 10 in the manner above-described.

[0060] Notably, pressing first and second ion exchange membranes againstthe first and second side surfaces of the D-spacer 100 forms a D-chamber101. The inner peripheral edge 108 of the D-spacer perimeter 102 helpsdefine a space which functions as a fluid passage for aqueous liquidflowing through the D-chamber 101.

[0061] A first throughbore 110 and a second throughbore 112 are formedin the D-spacer and define fluid passages for the respective supply anddischarge of aqueous liquid in the D-chamber. The positions of the firstthroughbore 110 and second throughbore 112 of the D-spacer 100correspond to those of the first throughbore 20 and second throughbore22 of the C-spacer 10 respectively when the water purification apparatusis assembled. In this respect, the first throughbore 110 and secondthroughbore 112 of the D-spacer 100 communicate with the firstthroughbore 20 and second throughbore 22 of the C-spacer 10respectively. In operation, aqueous liquid is supplied from the firstthroughbore 110 of the D-spacer 100, flows through the D-chamber andbecomes purified, and is then discharged via the second throughbore 112of the D-spacer 100.

[0062] In one embodiment, the first and second throughbores 110 and 112of the D-spacer 100 are formed in the perimeter 102 of the D-spacer 100.To facilitate flow of water to be purified into the D-chamber via thefirst throughbore 110, a first plurality of channels 114 are formedthrough the perimeter 102 and provides for communication between thefirst throughbore 110 and the D-chamber. Similarly, a second pluralityof channels 116 are formed through the perimeter 102 and provides forcommunication between the second throughbore 112 and the D-chamber,thereby facilitating discharge of purified water from the D-chamber.

[0063] Although the D-spacer 100 has been described as being providedwith first and second throughbores 110 and 112, each associated with aplurality of channels 114 and 116, to effect fluid flow into and out ofthe D-chamber, it is understood that other means may be provided tosupply and discharge aqueous liquid in and out of the D-chamber. Forinstance, water to be purified may be introduced directly into theD-chamber via the a first throughbore formed in an ion exchangemembrane. Similarly, purified water may be discharged directly out ofthe D-chamber via a second throughbore formed in an ion exchangemembrane. In this respect, flows in and out of the D-chamber would bechannelled in a manner similar to that above-described for theC-chamber.

[0064] A third throughbore 118 extends through the surface of theD-spacer perimeter 102 and provides a fluid passage for aqueous liquiddischarging from a C-chamber. Further, a fourth throughbore 120 extendsthrough the surface of the D-spacer perimeter for supplying aqueousliquid to a C-chamber. The positions of the third throughbore 118 andfourth throughbore 120 of the D-spacer perimeter communicate with firstand second throughbores respectively formed in a C-chamber forfacilitating flow in and out of such C-chamber. In the embodimentillustrated in FIG. 3, the third and fourth throughbores 118 and 120 ofthe D-spacer perimeter 102 communicate with first and secondthroughbores respectively formed in an ion exchange membrane pressedagainst a C-spacer perimeter 112. In operation, aqueous liquid issupplied to a C-chamber via the third throughbore 118 of the D-spacerperimeter 102 and the first throughbore in the ion exchange membrane.Such aqueous liquid then flows through such C-chamber, becomes loadedwith ionic species migrating through the ion exchange membranes pressedagainst the C-spacer 10, and is discharged from the C-chamber via thesecond throughbore in the ion exchange membrane and the fourththroughbore in the D-spacer perimeter 102.

[0065] Throughgoing holes 122 a, 122 b, 123 a, and 123 b are alsoprovided in the perimeter of the D-spacer 100. Holes 122 a and 122 b areadapted to receive alignment rod which assists in aligning the D-spacer100 when assembling the water purification unit. Holes 123 a and 123 bare adapted to flow aqueous liquid discharging from the anode andcathode chambers.

[0066] As discussed above, a side surface of the D-spacer 100 isprovided with apertures 124 to receive insertion of bosses 32 associatedwith the C-spacer 10. Further, a groove 126 is also provided in a sidesurface of the D-spacer perimeter 102 to receive insertion of thesecondary sealing member 34. In one embodiment, the apertures 124 andthe groove 126 is provided on both the first and second side surfaces ofthe D-spacer perimeter 102.

[0067] A first flange 128 and a second flange 130 can depend from a sidesurface of the perimeter 102 of the D-spacer 100 and surround the firstthroughbore 110 and second throughgoing bore 112 of the D-spacer 100respectively. When the water purification apparatus is assembled, thefirst flange 128 engages and pinches a portion of the C-spacer perimeter12 surrounding the first throughgoing bore 20 of the C-spacer 10.Similarly, the second flange 130 engages and pinches a portion of theC-spacer 10 surrounding the second throughgoing bore 22 of the C-spacerperimeter 12. In one embodiment, first and second flanges 128 and 130are provided on both side surfaces of the D-spacer 100 to engage andpinch adjacent C-spacers 10 on each side of the D-spacer 100.

[0068] A first upstanding shallow ridge 132 and a second upstandingshallow ridge 134 can be provided extending from a side surface of theperimeter 102 of the D-spacer 100. The first and second upstandingshallow ridges 132 and 134 are provided to prevent or reduce ingress ofaqueous liquid from the D-chamber 101 and into the third and fourththroughbores 118 and 120 of the D-spacer 100. Aqueous liquid in theD-chamber 101 may leak into any of the third and fourth throughbores 118and 120 if the ion exchange membrane adjacent to the D-spacer 100disengages from the D-spacer perimeter 102, thereby creating a flow pathfor liquid in D-chamber 101 to flow into any of the third or fourththroughbores 118 and 120, thereby providing a risk for mixing of D-flowwith C-flow. To reduce the likelihood that the ion exchange membranebecomes disengaged from the D-spacer perimeter 102, one or moreupstanding shallow ridges can be strategically provided on the D-spacerperimeter 102 (two upstanding shallow ridges 132 and 134 are provided inthe embodiment illustrated in FIG. 4) to engage and compress a sidesurface of ion exchange membrane against the C-spacer mesh 26 when theunit is assembled, thereby providing a more effective seal between theion exchange membrane and the D-spacer 100.

[0069] More particularly, the upstanding shallow ridges 132 and 134 arepositioned on the D-spacer perimeter 102 to compress a portion of thefirst side surface of ion exchange membrane at a location opposite tothat of the location of the second side surface portion which is notseated against the C-spacer perimeter 12 but which is engaged toD-spacer perimeter 102 (hereinafter, surface portion). Further, theupstanding shallow ridges must necessarily compress that part of surfaceportion which is disposed between throughbore of ion exchange membraneand the inner peripheral edge of the D-spacer perimeter 102. When theunit is assembled, portions of the second side surface of ion exchangemembrane are firmly pressed against C-spacer perimeter 12, andparticularly against the recess portion 30 of the C-spacer perimeter 12,by virtue of contact between the first side surface of ion exchangemembrane and a side surface of the D-spacer perimeter 102. Thoseportions of the ion exchange membrane which are not firmly pressedagainst the C-spacer perimeter recess 30 are disposed against theC-spacer mesh 26. Because the mesh 26 is subject to buckling or otherdeformation, the ion exchange membrane disposed against the mesh 26 ismore likely to disengage from the surface of the D-spacer perimeter 102than that portion of the ion exchange material pressed against therecess 30. Where this disengagement occurs at the inner peripheral edgeof the D-spacer perimeter 102, and continues along the D-spacerperimeter surface to either of throughbores 118 or 120, fluidcommunication is established between D-chamber 101 and throughbores 118and 120, creating a potential for mixing of D-flow and C-flow. Bypositioning upstanding shallow ridges 132 and 134 as above-described,buckling of mesh 26 is prevented or reduced, and the risk that thisflowpath becomes established is mitigated. Preferably, the upstandingshallow ridge traverses the entire surface portion between oppositeedges of ion exchange membrane.

[0070] In one embodiment, upstanding shallow ridges 132 and 134 areprovided on both the first and second sides of the D-spacer perimeter102 at positions as above-described.

[0071] In this way, ion exchange membranes are compressed against bothsides of the C-spacer mesh 26, thereby resisting buckling of theC-spacer mesh 26.

[0072] Flanges 136 and 138 are also provided and extend from a sidesurface of the D-spacer perimeter 102 and surround holes 123 a and 123b. Similarly, flanges 140 and 142 are also provided extending from theD-spacer perimeter 102 about throughbore 118 and 120. When the waterpurification device is assembled, flanges 126, 128, 140 and 142 engageand pinch a portion of C-spacer 10. In this manner, flanges 126 and 128prevent or reduces the mixing of D-flow with C-flow in the event thation exchange membrane disengages from D-spacer perimeter 102 surface, asabove-described, thereby providing a flow path from the D-chamber 101.On the other hand, flanges 140 and 142 facilitate better sealing offlanges 128 and 130 against C-spacer perimeter 12. Without flanges 140and 142, the sealing features about throughbores 110 and 118 or 112 and120 may not be perfectly vertically aligned, which could compresssealing of these throughbores.

[0073] Where the water purification apparatus is an electrodeionizationunit, ion exchange resin is provided in the D-chamber and positionedbetween the anion and cation exchange membranes provided on either sideof the D-spacer 100. Alternatively, where no ion exchange resin isrequired, such as in the case of an electrodyalisis unit, a mesh can beprovided in much the same manner as provided in the above-describedC-spacer 10, for purposes of spacing ion exchange membranes disposed oneither side of the D-spacer 100.

[0074] It is understood that the above-described embodiments of aD-spacer 100 could be used as C-spacers 10 in electrically driven waterpurification units. Similarly, the above-described embodiments of aC-spacer 10 could be used as D-spacers 100 in such units.

[0075] Referring to FIG. 6, an electrode end plate 200, such as acathode end plate 200 a or an anode end plate 200 b, (an anode end plate200 b), comprises a hard, solid plastic material, having a first sidesurface 202 and an opposing second side surface (not shown). The firstside surface 200 comprises a perimeter 204 having an inner peripheraledge 206 which defines an interior recessed portion 208. The second sidesurface can be substantially planar. In order to complement the sealingfeatures provided on the above-described embodiment of the C-spacer 10,and therefore improves sealing of the C-chamber and the electrodechamber, the electrode end plate 200 is made of harder material than theC-spacer 10. Suitable materials for the electrode end plate 200 includepolyethylene and polypropylene.

[0076] The first side surface 202 can be pressed against an ion exchangemembrane, such as a cation exchange membrane 6 or an anion exchangemembrane 4. In one embodiment, the ion exchange membrane pressed againstthe first side surface 202 is also pressed against a side surface of aC-spacer 10. Notably, pressing an ion exchange membrane against thefirst side surface of the electrode end plate 200 forms an electrodechamber, such as a cathode chamber or an anode chamber.

[0077] As discussed above, and in likewise manner with the D-spacers 100of the first side surface 202 of the electrode end plate 200 is providedwith apertures 210 to receive insertion of bosses 32 associated withC-spacer 10. Further, a groove 212 is also provided in the first sidesurface of the electrode end plate 200 to receive insertion of thesecondary sealing member 34.

[0078] Where throughgoing bores 214 and 216 are provided in theelectrode end plate to facilitate D-flow, as is the case in theelectrode end plate 200 illustrated in FIG. 6, a first flange 218 and asecond flange 220 can extend from the first side surface 202 of theperimeter 204 of the electrode end plate 200 and surround thethroughgoing bores 214 and 216 of the electrode end plate 200. When thewater purification apparatus is assembled, the first flange 218 engagesand pinches a portion of the C-spacer 10 perimeter surrounding the firstthroughgoing bore 20 of the C-spacer 10. Similarly, the second flange220 engages and pinches a portion of the C-spacer 10 surrounding thesecond throughgoing bore 22 of the C-spacer perimeter 12. This serves toprevent or reduce mixing of D-flow with C-flow.

[0079] Referring to FIG. 2, the embodiment of the spacer illustratedtherein can be manufactured by injection moulding. Where the perimeter12 is comprised of a high temperature melt processible plastic such as athermoplastic vulcanizate, the perimeter is preferably overmolded on themesh by injection molding.

[0080] Where the C-spacer 10 is formed by overmolding mesh 26 withperimeter 12, the mesh 26 is first formed by conventional methods andthen interposed between cavity plate 302 and core plate 304 of mold 300.Referring to FIG. 7, while interposed between plates 302 and 304, andimmediately before the mold 300 is clamped together, mesh 26 issubjected to tensile forces such that the mesh 26 is substantiallyplanar and not slack when the mold 300 is clamped together. In thisrespect, tension should be provided along the axis indicated by arrow301. Where such tensile forces are absent, the mesh 26 may becomeconvoluted and remain in this shape when the mold 300 is clampedtogether. This may result in a C-spacer 10 having a convoluted meshportion 26, which makes it more difficult for the C-spacer 10 to formeffective seals with adjacent structural components.

[0081] Referring to FIGS. 7, 8, 9, and 10, in one embodiment, the mold300 is a three-plate mold comprising a sprue plate 306, a cavity plate302, and a core plate 304. An injection mold machine 316 is provided toinject feed material through sprue 308 in sprue/runner plate 306. Thesprue 308 comprises a throughbore which communicates with a runnersystem 310 (see FIG. 8) formed as an exterior surface 311 of cavityplate 302. The runners communicate with an interior of cavity 302through a plurality of gates 314 (see FIG. 9) drilled through cavityplate 302.

[0082] When the individual plates 302, 304 and 306 of mold 300 areclamped together, feed material injected by injection mold machine 316through sprue 308 flows through the runner system 310 and is directedvia gates 314 into impressions 318 and 320. Once inside cavity plate302, injected feed material fills the impressions 318 and 320 formed inthe interior surfaces 322 and 324 of cavity plate 302 and core plate 304respectively, such impressions being complementary to the features ofC-spacer perimeter 12. In filling the impressions, feed material flowsthrough mesh 26 which is clamped between core and cavity plates 302 and304.

[0083] To help define inner peripheral edge 18 of C-spacer 10, acontinuous ridge 326 depends from interior surface 322 of cavity plate302 defining a space 328 wherein feed material is prevented from flowinginto. Similarly, a complementary continuous ridge 330 depends frominterior surface 324 of core plate 304, defining a space 332 whereinfeed material is also prevented from flowing into space 328. To thisend, when cavity plate 302 and core plate 304 are clamped together,ridges 326 and 330 pinch opposite sides of mesh 26, thereby creating abarrier to flow of injected feed material. In doing so, such arrangementfacilitates the creation of inner peripheral edge 18 of C-spacerperimeter 12, to which mesh 26 is joined.

[0084] To injection mold the C-spacer embodiment illustrated in FIG. 2,the core and cavity plates 302 and 304 are clamped together, therebypinching mesh 26 therebetween. Conventional injection mold machines canbe used, such as a Sumitomo SH22OA™ injection mold machine. To begininjection molding, material used for manufacturing the C-spacerperimeter, such as a thermoplastic vulcanizate, is dropped from anoverhead hopper into the barrel of the machine where it is plasticizedby the rotating screw. The screw is driven backwards while the materialitself remains out in front between the screw and the nozzle.Temperature along the material pathway varies from approximately 380° F.where the material enters the screw to 400° F. immediately upstream ofthe mold 300.

[0085] To begin filling the mold 300, screw rotation is stopped, andmolten plastic is thrust forward in the direction of the screw axisthrough the nozzle 334, sprue 308 and mold gates. Once the mold 300 isfilled, injection pressure is maintained to pack out the part. Materialshrinkage occurs inside the mold 300 as the temperature is relativelylower than inside the barrel. As a result, pressure must be continuouslyapplied to fill in any residual volume created by shrinkage. When thepart is adequately packed and cooled, mold 300 is opened. The ejectorpins 336 are actuated, thereby releasing the part.

[0086]FIGS. 11, 12, 13 and 14 illustrate a second mold 400 which couldbe used to form C-spacer 10 by overmolding mesh 26 with perimeter 12.Mesh 26 is first formed by conventional methods and then interposedbetween cavity plate 402 and core plate 404 of mold 400. In particular,mesh 26 is suspended on hanging pins 401 which depend from interiorsurface 422 of cavity plate 402. To this end, mesh 26 is provided withthroughbores which receive hanging pins 401. In one embodiment, mesh 26is die cut to dimensions such that mesh 26 does not extend appreciablyinto perimeter 12 once perimeter 12 is formed within impression 418 and420 by injection molding using mold 400. In this respect, in anotherembodiment, mesh 26 does not extend across feature on the impressions418 and 420 which cause the formation of the secondary seal member 34.Interior surface 424 of core plate 404 is provided with depressions 405to receive and accommodate hanging pins 401 when mold 400 is clampedtogether.

[0087] Referring to FIGS. 11, 12, 13 and 14, in one embodiment, the mold400 is a three-plate mold comprising a sprue plate 406, a cavity plate402, and a core plate 404. An injection mold machine 416 is provided toinject feed material through sprue 408 in sprue plate 406. The sprue 408comprises a throughbore which communicates with a runner system 410 (seeFIG. 14) formed as an exterior surface 411 of cavity plate 402. Therunners communicate with an interior of cavity 402 through a pluralityof gates 414 (see FIG. 12) drilled through cavity plate 402.

[0088] When the individual plates 402, 404 and 406 of mold 400 areclamped together, feed material injected by injection mold machine 416through sprue 408 flows through the runner system 410 and is directedvia gates 414 into impressions 418 and 420. Once inside cavity plate402, injected feed material fills the impressions 418 and 420 formed inthe interior surfaces 422 and 424 of cavity plate 402 and core plate 404respectively, such impressions being complementary to the features ofC-spacer perimeter 12. In filling the impressions, feed material flowsthrough the perimeter of mesh 26 which is clamped between core andcavity plates 402 and 404.

[0089] To help define inner peripheral edge 18 of C-spacer 10, acontinuous ridge 426 depends from interior surface 422 of cavity plate402 to abut a side of mesh 26 defining an interior space 428 whereinfeed material is prevented from flowing thereinto. Similarly, acomplementary continuous ridge 430 conterminous with continuous ridge426 depends from interior surface 424 of core plate 404 to abut theopposite side of mesh 26, defining an interior space 432 wherein feedmaterial is also prevented from flowing into space 432. To this end,when cavity plate 402 and core plate 404 are clamped together, opposedconterminous ridges 426 and 430 pinch opposite sides of mesh 26, therebycreating a barrier to flow of injected feed material. In doing so, sucharrangement facilitates the creation of inner peripheral edge 18 ofC-spacer perimeter 12, to which mesh 26 is joined.

[0090] Using mold 400, injection molding of the C-spacer embodimentillustrated in FIG. 2 can be accomplished much in the same manner aswhen using above-described mold 300.

[0091] It will be understood, of course, that modification can be madein the embodiments of the invention described herein without departingfrom the scope and purview of the invention as defined by the appendedclaims.

1. A method of injection molding a thin plastic part comprising aperimeter having an inner peripheral edge and a mesh joined to saidinner peripheral edge, including the steps of (a) providing a moldhaving a cavity and a core, the cavity having a first interior surfaceand a first continuous ridge depending from the first interior surface,the core having a second interior surface and a second continuous ridgedepending from the second interior surface conterminous with the firstcontinuous ridge; (b) disposing a mesh having opposite sides between thecavity and the core; and (c) pinching opposite side of the mesh betweenthe ridges to form a flow barrier.
 2. The method as claimed in claim 1wherein the perimeter and the mesh are comprised of different materials.3. The method as claimed in claim 2 wherein the perimeter is comprisedof materials selected from the group consisting of thermoplasticvulcanizates, thermoplastic olefins, and fluoropolymers.
 4. The methodas claimed in claim, 2 wherein the perimeter is comprised of athermoplastic vulcanizate.
 5. The method as claimed in claim 3 whereinthe mesh is comprised of materials selected from the group consisting ofpolypropylene and polyethylene.
 6. The method as claimed in claim 4wherein the mesh is comprised of materials selected from the groupconsisting of polypropylene and polyethylene.
 7. The method as claimedin claim 6 wherein the mesh is not slack.
 8. The method as claimed inclaim 1 wherein the cavity further includes hanging pins depending fromthe first interior surface, and additionally comprising, in step (b),suspending the mesh from the hanging pins.